1. Technical Field
The present invention relates to providing wireless local area network (LAN) coverage enhancement using dynamic antennas.
2. Description of Related Art
FIG. 1 illustrates a wireless local area network (LAN) 100 including an access point 110 with an omnidirectional antenna pattern 150 in the prior art. The access point 110 transmits to stations 120 and 130 on the omnidirectional antenna pattern 150. The access point 110 cannot transmit to a station 140 located outside of the omnidirectional antenna pattern 150 with a radius 160. The omnidirectional antenna pattern 150 of the access point 110 is typically effective for broadcast communication to reach each of the stations (e.g., the stations 120 and 130) within the coverage area of the omnidirectional antenna pattern 150 and associated with the access point 110. However, although the omnidirectional antenna pattern 150 reaches the broadest group of stations (e.g., stations 120 and 130), the omnidirectional antenna pattern 150 does not reach far enough (e.g., further than the radius 160) to cover the station 140.
In an 802.11 implementation of the wireless LAN 100, portions of the 802.11 protocol, such as beacon frames, use broadcast communication to communicate with the stations 120 and 130. A beacon frame (or beacon) enables the stations 120 and 130 to establish and maintain communication in an orderly fashion with each other and with the access point 110. The beacon also serves a variety of management functions, one being to identify the presence of the access point 110 in the wireless LAN 100.
The stations 120, 130, and 140 passively scan radio frequency (RF) channels and listen for beacons coming from access points (e.g., the access point 110) in order to find and associate with the access point 110. The beacon also enables a ranking of multiple access points (not shown) based on the received signal strength of beacons from the multiple access points, along with information regarding the capabilities and data rates of the multiple access points. The stations 120, 130, and 140 may then associate with the most preferable access point of the multiple access points to the stations 120, 130, and 140 based on the beacons received from the multiple access points. After association with the most preferable access point, the stations 120, 130, and 140 typically continue to scan for beacons, for example, transmitted from the multiple access points (not shown), in case the signal from the currently-associated access point becomes too weak to maintain communication. The stations 120, 130, and 140 also may roam throughout a building or facility, and use the beacons from the multiple access points to make roaming decisions to associate with one of the multiple access points.
Another purpose of the beacon is to support the stations 120, 130, and 140 operating in power saving mode. For example, the stations 120 and 130 synchronize communication with the access point 110 before the stations 120 and 130 operate in the power savings mode. With infrastructure networks, the access point 110 will buffer frames destined for the sleeping stations 120 and 130 and announce in the beacon which of the stations 120 and 130 have data frames buffered in the access point 110. When the stations 120 and 130 wake up from the power savings mode, the stations 120 and 130 retrieve the buffered frames from the access point 110.
Therefore, without beacons, communication within the wireless LAN 100 becomes difficult. For example, because the station 140 is located outside the omnidirectional antenna pattern 150, the station 140 does not receive beacons transmitted from the access point 110. The station 140 therefore cannot associate with the access point 110. The station 140 also cannot communicate with the stations 120 and 130 through the access point 110. The station 140 further cannot synchronize communication with the access point 110 in order to operate in power savings mode. Furthermore, the station 140 may disrupt communication between the access point 110 and the stations 120 and 130 through transmission that collide over the shared medium of the wireless LAN 100 with transmissions of the access point 110 and the stations 120 and 130.